Matt , uv stable , flame-retardant co-extruded polyester film, a method for the production thereof and the use of the same

ABSTRACT

The invention relates to a co-extruded, biaxially oriented polyester film consisting of a base layer and at least one outer layer. The film contains at least one flame-retardant agent, at least one UV-stabilizer and has a matt outer layer which contains a mixture and/or a blend of two components (I) and (II), whereby component (I) is substantially a polyethylene terephthalate homopolymer, or a polyethylene terephthalate copolymer, or a mixture of polyethylene terephthalate homopolymers or polyethylene terephthalate copolymers, and component (II) is a polymer containing at least one sulphonate group.

[0001] The invention relates to a biaxially oriented polyester film witha base layer composed of at least 70% by weight of a thermoplasticpolyester and comprising at least one UV stabilizer and one flameretardant, and with at least one matt outer layer which comprises amixture or, respectively, a blend made from two components I and II. Theinvention further relates to the use of the film and to a process forits production.

[0002] Component I of the mixture or blend is a polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer, or amixture of polyethylene terephthalate homo- or copolymers.

[0003] Component II of the mixture or blend is a polyethyleneterephthalate copolymer which is composed of the condensation product ofthe following monomers or, respectively, of their derivatives capable offorming polyesters: isophthalic acid, aliphatic dicarboxylic acid,sulfomonomer which contains a metal sulfonate group on the aromaticmoiety of an aromatic dicarboxylic acid, and aliphatic or cycloaliphaticglycol.

[0004] The outer layer of the invention has a characteristic mattsurface or appearance and is very suitable for use in constructingexhibition stands, in greenhouses, or for industrial applications, inparticular where a requirement is UV resistance or impermeability to UVlight and flame retardancy to DIN 4102 Part 2, construction materialsclass B2 and B1.

BACKGROUND OF THE INVENTION

[0005] There is high industrial demand for transparent, high-glossplastic films, e.g. biaxially oriented propylene films or biaxiallyoriented polyester films. There is also an increasing demand fortransparent films of this type which are flame retardant to DIN 4102 andwhich have at least one surface layer which is not high-gloss but has acharacteristic matt appearance and therefore, for example, provides theapplication with an appearance which is particularly attractive andtherefore effective for promotional purposes, and provides protectionfrom UV radiation while also providing flame retardancy.

[0006] U.S. Pat. No. 4,399,179 describes a coextruded biaxially orientedpolyester film which is composed of a transparent base layer and of atleast one matt layer which essentially consists of a certainpolyethylene terephthalate copolymer and also comprises inert particleswith a diameter of from 0.3 to 20 pm at a concentration of from 3 to40%. The specific copolymer is a processing aid which reduces theviscosity of the melt comprising the inert particles, thus permittingsatisfactory extrusion of that layer. The mattness of the film isachieved by adding the inert particles to the appropriate layer.

[0007] EP 0 144 978 describes a self-supporting oriented film made fromthermoplastic and, on at least one of its two surfaces, bearing acontinuous polyester coating which is applied as aqueous dispersion tothe film prior to the final stretching step. The polyester coating iscomposed of a condensation product of various monomers which are capableof forming polyesters, such as isophthalic acid, aliphatic dicarboxylicacid, sulfomonomers, and aliphatic or cycloaliphatic glycols.

[0008] EP-A-0 620 245 describes films with improved heat resistance.These films comprise antioxidants which are suitable for scavenging freeradicals formed in the film and degrading any peroxide formed. However,that specification gives no proposal as to how the UV resistance offilms of that type might be improved.

[0009] DE-A 2346 787 describes a flame-retardant, phospholane-modifiedpolymer. Besides the polymer, the use of the polymer to give films andfibers is also claimed. When films were produced from thisphospholane-modified polymer the following shortcomings were apparent:

[0010] The polymer is very susceptible to hydrolysis and has to be veryeffectively predried. When the polymer is dried with prior art dryers itcakes, and production of a film is therefore possible only under verydifficult conditions.

[0011] The films produced, under extreme and uneconomic conditions, alsoembrittle at high temperatures. The associated decline in mechanicalproperties is so severe as to make the film unusable. This embrittlementoccurs after as little as 48 hours of exposure to heat.

[0012] The instances described give no indication as to how at least onesurface of the film can be provided with low gloss while retaining highfilm transparency, or how the film is to absorb UV light, or how thefilm is to be provided with high UV resistance and also flameretardancy.

[0013] It was therefore an object of the present invention to provide acoextruded biaxially oriented and transparent polyester film which hasat least one matt outer layer and whose production is simple andcost-effective, and which has the good physical properties of knownfilms, causes no disposal problems, and in particular absorbs UV lightand has high UV resistance, and also is flame-retardant to DIN 4102, anddoes not embrittle on exposure to heat.

BRIEF DESCRIPTIONS OF THE INVENTION

[0014] This object is achieved by means of a coextruded and biaxiallyoriented polyester film of the generic type mentioned at the outset, thecharacterizing features of which are that the film comprises at leastone UV stabilizer and at least one flame retardant, the flame retardantand, where appropriate, the UV stabilizer being fed by way ofmasterbatch technology, and has a matt outer layer which comprises amixture or, respectively, a blend made from two components I and II.

DETAILED DESCRIPTION OF THE INVENTION

[0015] Component I of the mixture or blend is a polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer, or amixture made from polyethylene terephthalate homo- or copolymers.

[0016] Component II of the copolymer or of the mixture or blend is apolymer containing at least one sulfonate group, in particular acondensation product of the following monomers or of their derivativescapable of forming polyesters:

[0017] A) from 65 to 95 mol % of isophthalic acid;

[0018] B) from 0 to 30 mol % of at least one aliphatic dicarboxylic acidwith the formula

HOOC(CH₂)_(n)COOH

[0019] where

[0020] n is from 1 to 11;

[0021] C) from 5 to 15 mol % of at least one sulfomonomer containing analkali metal sulfonate group on the aromatic moiety of a dicarboxylicacid;

[0022] D) a copolymerizable aliphatic or cycloaliphatic glycol havingfrom 2 to 11 carbon atoms, in the stoichiometric amount necessary toform 100 mol % of condensate;

[0023] where each of the percentages given is based on the total amountof the monomers forming component II.

[0024] High UV resistance means that sunlight or other UV radiationcauses no, or only extremely little, damage to the films, and that thefilms are therefore suitable for outdoor applications and/or criticalindoor applications. In particular, the films should not yellow after anumber of years of outdoor use, nor display any embrittlement orcracking of the surface, nor should their mechanical propertiesdeteriorate. High UV resistance therefore means that the film absorbs UVlight and does not transmit light until the visible region has beenreached.

[0025] The good mechanical properties include high modulus of elasticity(E_(MD)>3200 N/mm²; E_(TD)>3500 N/mm²) and also good values for tensilestrength at break (in MD>100 N/mm²; in TD>130 N/mm²).

[0026] Good orientability includes the capability of the film to giveexcellent orientation both longitudinally and transversely during itsproduction, without break-offs.

[0027] Cost-effective production includes the capability of the rawmaterials or raw material components needed for producing theflame-retardant film to be dried using conventional industrial dryers.It is important that the raw materials do not cake or undergo thermaldegradation. These prior art industrial dryers include vacuum dryers,fluidized-bed dryers, and fixed-bed dryers (tower dryers). These dryersoperate at temperatures from 100 to 170° C., at which polymers providedwith flame retardancy by conventional methods cake and eventually haveto be removed by force, making film production impossible.

[0028] In the case of the vacuum dryer, which has the gentlest dryingaction, the raw material usually passes through a range of temperaturesfrom about 30 to 130° C. at a subatmospheric pressure of 50 mbar. Thishas to be followed by what is known as post-drying in a hopper attemperatures from 100 to 130° C. with a residence time of from 3 to 6hours. Even here, the known polymers cake to an extreme extent.

[0029] No embrittlement on short exposure to heat means that after 100hours of controlled heating at 100° C. in a circulating-air dryingcabinet the film has not embrittled and does not have poor mechanicalproperties.

[0030] For the purposes of the present invention, mixtures aremechanical mixtures prepared from the individual components. For this,the individual constituents are generally combined in the form ofsmall-dimensioned compressed moldings, e.g. lenticular or bead-shapedpellets, and mixed with one another mechanically, using a suitableagitator. Another way of producing the mixture is to feed components Iand II in pellet form separately to the extruder for the outer layer ofthe invention, and to carry out the mixing in the extruder and/or in thedownstream systems for transporting the melt.

[0031] For the purposes of the present invention, a blend is analloy-like composite of the individual components I and II which can nolonger be separated into the initial constituents. A blend hasproperties like those of a homogeneous material and can therefore becharacterized by appropriate parameters.

[0032] According to the invention, the film has at least two layers. Thelayers which it then encompasses are a layer B (=base layer) and theouter layer A of the invention. In one preferred embodiment of theinvention, the film has a three-layer structure, and has the outer layerA on one side of the layer B (=base layer) and has another layer C onthe other side of the layer B. In this case, the two layers A and C formthe outer layers A and C. According to the invention, the UV stabilizerand the flame retardant may be present in the outer layer(s) and/or inthe base layer.

[0033] The base layer B of the film is preferably composed of at least70% by weight of a thermoplastic polyester. Polyesters suitable for thispurpose are those made from ethylene glycol and terephthalic acid(=polyethylene terephthalate, PET), from ethylene glycol andnaphthalene-2,6-dicarboxylic acid (=polyethylene 2,6-naphthalate, PEN),from 1,4-bishydroxymethylcyclohexane and terephthalic acid(=poly-1,4-cyclohexanedimethylene terephthalate, PCDT), or else madefrom ethylene glycol, naphthalene-2,6-dicarboxylic acid andbiphenyl-4,4′-dicarboxylic acid (=polyethylene 2,6-naphthalatedibenzoate, PENBB). Particular preference is given to polyesters atleast 90 mol %, preferably at least 95 mol %, of which is composed ofethylene glycol units and terephthalic acid units, or of ethylene glycolunits and naphthalene-2,6-dicarboxylic acid units. The remaining monomerunits derive from those other aliphatic, cycloaliphatic or aromaticdiols and dicarboxylic acids. Other examples of suitable aliphatic diolsare diethylene glycol, triethylene glycol, aliphatic glycols of theformula HO—(CH₂)_(n)—OH, where n is an integer from 3 to 6 (inparticular 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol and1,6-hexanediol) and branched aliphatic glycols having up to 6 carbonatoms. Among the cycloaliphatic diols, mention should be made ofcyclohexanediols (in particular 1,4-cyclohexanediol). Examples of othersuitable aromatic diols have the formula HO—C₆H₄—X—C₆H₄—OH, where X is—CH₂—, —C(CH₃)₂—, —C(CF₃)₂—, —O—, —S— or —SO₂—. Bisphenols of theformula HO—C₆H₄—C₆H₄—OH are also very suitable.

[0034] Other aromatic dicarboxylic acids are preferablybenzenedicarboxylic acids, naphthalene dicarboxylic acids (such asnaphthalene-1,4- or -1,6-dicarboxylic acid), biphenyl-x,x′-dicarboxylicacids (in particular biphenyl-4,4′-dicarboxylic acid),diphenylacetylene-x,x′-dicarboxylic acids (in particulardiphenylacetylene-4,4′-dicarboxylic acid) or stilbene-x,x′-dicarboxylicacids. Among the cycloaliphatic dicarboxylic acids mention should bemade of cyclohexanedicarboxylic acids (in particularcyclohexane-1,4-dicarboxylic acid). Among the aliphatic dicarboxylicacids, the C₃-C₁g alkanediacids are particularly suitable, and thealkane moiety here may be straight-chain or branched.

[0035] One way of preparing the polyesters is the transesterificationprocess. Here, the starting materials are dicarboxylic esters and diols,which are reacted using the customary transesterification catalysts,such as the salts of zinc, of calcium, of lithium, of magnesium or ofmanganese. The intermediates are then polycondensed in the presence ofwell-known polycondensation catalysts, such as antimony trioxide ortitanium salts. Another equally good preparation method is the directesterification process in the presence of polycondensation catalysts.This starts directly from the dicarboxylic acids and the diols.

[0036] At least one outer layer of the multilayer film of the inventioncomprises a mixture or, respectively, a blend made from two components Iand II and described in more detail below, and, where appropriate,comprises additives.

[0037] Component I of the outer layer mixture or of the blendessentially consists of a thermoplastic polyester, in particular thepolyester described in more detail for the base layer. A method whichhas proven successful here for achieving a high degree of mattness is touse a polyester of comparatively low viscosity for component I of theouter layer of the invention. To describe the viscosities of the meltsuse is made of a modified solution viscosity (SV or “standardviscosity”). The SVs of commercially available polyethyleneterephthalates suitable for producing biaxially oriented films are inthe range from 500 to 1200. A method which has proven successful forobtaining a high degree of film mattness for the purposes of the presentinvention is to use polymers whose SV is in the range from 500 to 800,preferably in the range from 500 to 750, particularly preferably in therange from 500 to 700, for component I of the outer layer of theinvention.

[0038] As stated above, component II of the outer layer mixture isobtained by condensation of the following monomers or of theirderivatives capable of forming polymers:

[0039] A) isophthalic acid,

[0040] B) if appropriate, an aliphatic dicarboxylic acid of the formula

HOOC(CH₂)_(n)COOH

[0041] where

[0042] n is in the range from 1 to 11,

[0043] C) a sulfomonomer containing an alkali metal sulfonate group onthe aromatic moiety of an aromatic dicarboxylic acid, and

[0044] D) an aliphatic or cycloaliphatic glycol having from 2 to 11carbon atoms, in the amount needed to form 100 mol % of condensate.

[0045] The total molar equivalents of acid present should besubstantially the same as the total equivalents of glycol present.

[0046] Examples of dicarboxylic acids suitable as component B) of thecopolyesters are malonic, adipic, azelaic, glutaric, sebacic, suberic,succinic and brassylic acid, and also mixtures of these acids or theirderivatives capable of forming polyesters. Of the abovementioned acids,sebacic acid is preferred.

[0047] Examples of sulfomonomers which contain a metal sulfonate groupon the aromatic moiety of an aromatic dicarboxylic acid (component C)are monomers of the following formula:

[0048] where

[0049] M is a monovalent cation of an alkali metal,

[0050] Z is a trivalent aromatic radical, and

[0051] X and Y are carboxy groups or polyester-forming equivalents.

[0052] Monomers of this type are described in U.S. Pat. No. 3,563,942and 3,779,993. Examples of monomers of this type are the sodium salts ofsulfoterephthalic acid, of 5-sulfoisophthalic acid, of sulfophthalicacid, of 5-(p-sulfophenoxy)isophthalic acid, or of5-sulfopropoxyisophthalic acid, and similar monomers, and alsoderivatives of these, such as the dimethyl esters, capable of formingpolyesters. M is preferably Na⁺, Li⁺, or K⁺.

[0053] The term “derivatives capable of forming polyesters” here meansreaction participants with groups capable of condensation reactions, inparticular transesterification reactions, to form polyester bonds.Groups of this type include carboxy groups. They also include the loweralkyl esters of these, e.g. dimethyl terephthalate, diethylterephthalate, and numerous other esters, halides, and salts. The acidmonomers are preferably used in the form of dimethyl esters, since thispermits better control of the condensation reaction.

[0054] Examples of glycols suitable as component D) are ethylene glycol,1,5-pentanediol, 1 ,6-hexanediol, neopentyl glycol, 1,10-decanediol,cyclohexanedimethanol, and similar substances. It is preferable to useethylene glycol.

[0055] The copolyesters may be prepared by known polymerizationtechniques. The procedure is generally to combine the acid componentswith glycol and to heat these in the presence of an esterificationcatalyst, with subsequent addition of a polycondensation catalyst.

[0056] The quantitative ratios of components A, B, C, and D used toprepare the mixtures of the invention have been found to be decisive forobtaining the matt outer layer. For example, at least about 65 mol % ofisophthalic acid (component A) has to be present as acid component.Component A is preferably from about 70 to 95 mol % of pure isophthalicacid.

[0057] As far as component B is concerned, any acid with the formulamentioned gives satisfactory results, and preference is given to adipicacid, azelaic acid, sebacic acid, malonic acid, succinic acid, glutaricacid, and mixtures of these acids. The desired amount within the rangegiven is preferably from 1 to 20 mol %, based on the acid components ofthe mixture II, if component B is present in the composition.

[0058] The amount of the glycol component present is stoichiometric.

[0059] The copolyesters suitable for the purposes of the invention alsohave an acid value below 10, preferably from 0 to 3, an averagemolecular weight below about 50,000, and an SV in the range from about30 to 700, preferably from about 350 to 650.

[0060] The ratio (ratio by weight) of the two components I and II of theouter layer mixture or blend may vary within wide limits and depends onthe intended use of the multilayer film. The ratio of components I andII is preferably in the range from I:II=10:90 to I:II=95:5, preferablyfrom I:II=20:80 to I:II=95:5, and in particular from I:II=30:70 toI:II=95:5.

[0061] According to the invention, the film comprises a UV stabilizerand a flame retardant. The UV stabilizer is advantageously fed by way ofwhat is known as masterbatch technology directly during film production,the concentration of the UV stabilizer here preferably being from 0.01to 5% by weight, based on the weight of the layer of the crystallizablethermoplastic.

[0062] According to the invention, the flame retardant is likewise fedby way of what is known as masterbatch technology directly during filmproduction, the concentration here being from 0.5 to 30% by weight,preferably from 1 to 20% by weight, based on the weight of the layer ofthe crystallizable thermoplastic.

[0063] Light, in particular the ultraviolet content of solar radiation,i.e. the wavelength region from 280 to 400 nm, causes degradation inthermoplastics, the results of which are not only a change in appearancedue to color change or yellowing but also an adverse effect onmechanical and physical properties.

[0064] The suppression of this photooxidative degradation is ofconsiderable industrial and economic importance, since without it manythermoplastics have drastically reduced scope of application.

[0065] The absorption of UV light by polyethylene terephthalates, forexample, starts below 360 nm, increasing markedly below 320 nm, and isvery pronounced below 300 nm. Maximum absorption occurs at between 280and 300 nm.

[0066] In the presence of oxygen it is mainly chain cleavage which isobserved, but without any crosslinking. The predominant photooxidationproducts in quantity terms are carbon monoxide, carbon dioxide andcarboxylic acids. Besides direct photolysis of the ester groups,attention has to be paid to oxidation reactions which proceed viaperoxide radicals, again to form carbon dioxide.

[0067] In photooxidation of polyethylene terephthalates there can alsobe cleavage of hydrogen at the position a to the ester groups, givinghydroperoxides and decomposition products of these, and this may beaccompanied by chain cleavage (H. Day, D. M. Wiles, J. Appl. Polym. Sci.16 [1972] p. 203).

[0068] UV stabilizers, i.e. light stabilizers which are UV absorbers,are chemical compounds which can intervene in the physical and chemicalprocesses of light-induced degradation. Carbon black and other pigmentscan give some protection from light, but these substances are unsuitablefor transparent films, since they cause discoloration or color change.For transparent, matt films the only suitable compounds are organic ororganometallic compounds which give rise to no, or only extremelyslight, color or color change in the thermoplastic to be stabilized,i.e. are soluble in the thermoplastic.

[0069] UV stabilizers which are suitable light stabilizers are thosewhich absorb at least 70%, preferably 80%, particularly preferably 90%,of the UV light in the wavelength region from 180 to 380 nm, preferablyfrom 280 to 350 nm. These are particularly suitable if they arethermally stable, i.e. do not decompose, nor cause any evolution of gas,in the temperature range from 260 to 300° C.

[0070] Examples of UV stabilizers which are suitable light stabilizersare 2-hydroxybenzophenones, 2-hydroxybenzotriazoles, organonickelcompounds, salicylic esters, cinnamic ester derivatives, resorcinolmonobenzoates, oxanilides, hydroxybenzoic esters, sterically hinderedamines and triazines, preference being given to the2-hydroxybenzotriazoles and the triazines.

[0071] The film of the invention comprises at least one flame retardant,fed by way of what is known as masterbatch technology directly duringfilm production, the concentration of the flame retardant being in therange from 0.5 to 30.0% by weight, preferably from 1.0 to 20.0% byweight, based on the weight of the layer of the crystallizablethermoplastic. The ratio by weight of flame retardant to thermoplasticusually maintained when producing the masterbatch is in the range from60:40 to 10:90.

[0072] Typical flame retardants include bromine compounds,chloroparaffins and other chlorine compounds, antimony trioxide, andalumina trihydrates, but the halogen compounds are disadvantageous dueto the halogen-containing by-products produced. Another extremedisadvantage is the low lightfastness of any film provided with these,and also the evolution of hydrogen halides in the event of a fire.

[0073] Examples of suitable flame retardants used according to theinvention are organophosphorus compounds, such as carboxyphosphinicacids, anhydrides of these, and dimethyl methylphosphonate. It isimportant for the invention that the organophosphorus compound issoluble in the thermoplastic, since otherwise compliance with therequired optical properties is lacking.

[0074] Since the flame retardants generally have some degree ofsusceptibility to hydrolysis, the additional use of a hydrolysisstabilizer can be advisable.

[0075] The hydrolysis stabilizers generally used are phenolicstabilizers, alkali metal/alkaline earth metal stearates, and/or alkalimetal/alkaline earth metal carbonates, in amounts of from 0.01 to 1.0%by weight. The amount used of phenolic stabilizers is preferably from0.05 to 0.6% by weight, in particular from 0.15 to 0.3% by weight, andtheir molar mass is preferably more than 500 g/mol. Pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or1,3,5-trimethyl-2,4,6-tris(3,5-di-tert-butyl-4-hydroxybenzyl)benzene isparticularly advantageous.

[0076] In one particularly preferred embodiment, the film of theinvention comprises from 1 to 20% by weight of a flame retardant, suchas dimethyl methylphosphonate and from 0.01 to 5.0% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol of the formula

[0077] or from 0.01 to 5.0% by weight of2,2-methylenebis(6-(2H-benzotriazol-2-yl)-4-(1,1,2,2-tetramethylpropyl)-phenol)of the formula

[0078] In one preferred embodiment, use may also be made of a mixture ofthese two UV stabilizers, or of a mixture of at least one of these twoUV stabilizers with other UV stabilizers, the total concentration oflight stabilizer preferably being from 0.01 to 5.0% by weight, based onthe weight of crystallizable polyethylene terephthalate.

[0079] Besides the flame retardant fed by way of masterbatch technologyand the UV stabilizer, the base layer and/or the outer layer(s) may alsocomprise conventional additives, such as stabilizers and antiblockingagents. They are advantageously added to the polymer or polymer mixturebefore melting begins. Examples of stabilizers used are phosphoruscompounds, such as phosphoric acid or phosphoric esters. Typicalantiblocking agents (also termed pigments in this context) are inorganicand/or organic particles, such as calcium carbonate, amorphous silica,talc, magnesium carbonate, barium carbonate, calcium sulfate, bariumsulfate, lithium phosphate, calcium phosphate, magnesium phosphate,aluminum oxide, lithium fluoride, the calcium, barium, zinc, ormanganese salts of the dicarboxylic acids used, carbon black, titaniumdioxide, kaolin, or crosslinked polymer particles, such as polystyreneparticles or acrylate particles.

[0080] Additives selected may also be mixtures of two or more differentantiblocking agents, or mixtures of antiblocking agents of the samecomposition, but with different particle sizes. The usual concentrationof the particles may be added to each of the layers, e.g. in the form ofa glycolic dispersion during polycondensation or by way of masterbatchesduring extrusion. Pigment concentrations which have proven particularlysuitable are from 0.0001 to 10% by weight. Addition of these particlesto the outer layer gives another advantageous opportunity of varying thedegree of mattness of the film. Increase in pigment concentration isgenerally associated with an increase in the degree of mattness of thefilm. An example of a detailed description of antiblocking agents isfound in EP A 0 602 964.

[0081] The present invention also provides a process for producing thisfilm. It encompasses

[0082] a) producing a film from base and outer layer(s) by coextrusion,

[0083] b) biaxial orientation of the film, and

[0084] c) heat-setting of the oriented film.

[0085] It is important for the invention that the masterbatch whichcomprises the flame retardant and, where appropriate, the hydrolysisstabilizer is precrystallized or predried. This predrying includesgradual heating of the masterbatch at subatmospheric pressure (from 20to 80 mbar, preferably from 30 to 60 mbar, in particular from 40 to 50mbar), with stirring, and, where appropriate, post-drying at constantincreased temperature, again at subatmospheric pressure. The masterbatchis preferably charged at ambient temperature from a feed vessel in therequired blend together with the polymers of the base and/or outerlayers and, where appropriate, with other raw material componentsbatchwise into a vacuum dryer which during the course of the drying orresidence time passes through a temperature profile of from 10 to 160°C., preferably from 20 to 150° C., in particular from 30 to 130° C.During a residence time of about 6 hours, preferably 5 hours, inparticular 4 hours, the raw material mixture is stirred at from 10 to 70rpm, preferably from 15 to 65 rpm, in particular from 20 to 60 rpm. Theresultant precrystallized or predried raw material mixture is post-driedin a downstream vessel, likewise evacuated, at from 90 to 180° C.,preferably from 100 to 170° C., in particular from 110 to 160° C., forfrom 2 to 8 hours, preferably from 3 to 7 hours, in particular from 4 to6 hours.

[0086] To produce the outer layer of the invention, it is advantageousto feed pellets of mixture component I and pellets of mixture componentII in the desired mixing ratio directly to the extruder, whereappropriate together with the flame retardant masterbatch which has beenpredried. It has proven advantageous for extrusion of the matt outerlayer of the invention to use a twin-screw extruder, e.g. as describedin EP 0 826 478. The materials can be melted and extruded at about 300°C. with a residence time of about 5 min. Under these conditions,transesterification reactions can proceed in the extruder, and these canform other copolymers from the homopolymers and the copolymers.

[0087] The polymers for the base layer are advantageously fed by way ofanother extruder, together with the flame retardant masterbatch, whichhas been predried. Any foreign bodies or contamination present may befiltered out from the polymer melt prior to extrusion. The melts arethen extruded through a coextrusion die to give flat melt films andlaminated to one another. The multilayer film is then drawn off andsolidified with the aid of a chill roll and, where appropriate, otherrolls.

[0088] The biaxial orientation is generally carried out sequentially orsimultaneously.

[0089] In sequential stretching, it is preferable to orient firstlongitudinally (i.e. in machine direction) and then transversely (i.e.perpendicularly to machine direction). This leads to orientation of themolecular chains. The longitudinal orientation can be carried out withthe aid of two rolls running at different speeds corresponding to thedesired stretching ratio. For transverse orientation use is generally inthe range made of an appropriate tenter frame. In simultaneousstretching the film is simultaneously stretched longitudinally andtransversely in a tenter frame.

[0090] The temperature at which the orientation is carried out may varywithin a relatively wide range and depends on the desired properties ofthe film. The longitudinal stretching is generally carried out at from80 to 130° C. and the transverse stretching at from 90 to 150 C. Thelongitudinal orientation ratio is generally in the range from 2.5:1 to6:1, preferably from 3:1 to 5.5:1. The transverse stretching ratio isgenerally in the range from 3.0:1 to 5.0:1, preferably from 3.5:1 to4.5:1. If desired, the transverse stretching may be followed by anotherlongitudinal orientation, and even by another transverse orientation.

[0091] In the heat-setting which follows, the film is held at atemperature of from 150 to 250° C. for from 0.1 to 10 s. The film isthen wound up in the usual way.

[0092] One or both surfaces of the film may therefore have a coating.The thickness of this coating on the finished film is from 5 to 100 nm,preferably from 20 to 70 nm, in particular from 30 to 50 nm. It ispreferably applied in-line, i.e. during the film-production process,advantageously prior to transverse orientation. Application by reversegravure roll coatings is particularly preferred, and this processpermits extremely uniform application of the coating at the layerthickness mentioned. The coatings are applied—preferably by aqueousmethods—as solutions, suspensions, or dispersions, and provide the filmsurface with additional functionality, for example making the filmsealable, printable, metallizable, sterilizable, antistatic, orimproving its aroma barrier for example, or permitting its adhesion tomaterials which would not otherwise adhere to the film surface (e.g.photographic emulsions). Examples of substances or compositions whichprovide additional functionality are:

[0093] Acrylates, as described by way of example in WO 94/13476,ethylene-vinyl alcohols, PVDC, waterglass (Na₂SiO₄), hydrophilicpolyesters (PET/IPA polyesters containing the sodium salt of5-sulfoisophthalic acid, for example as described in EP-A-0 144 878 orU.S. Pat. No. 4,252,885 or EP-A-0 296 620), vinyl acetates, for exampleas described in WO 94/13481, polyvinyl acetates, polyurethanes, thealkali metal or alkaline earth metal salts of C₁₀-C₁₈ fatty acids, andbutadiene copolymers with acrylonitrile or methyl methacrylate,methacrylic acid, acrylic acid, or esters thereof.

[0094] The compositions or substances mentioned are applied in the formof dilute, preferably aqueous, solution, emulsion, or dispersion to oneor both surfaces of the film. The solvent is then evaporated. If thecoatings are applied in-line prior to transverse stretching, the heattreatment during transverse stretching and subsequent heat-setting isusually sufficient to evaporate the solvent and dry the coating. Thedried coatings then have the abovementioned desired layer thicknesses.

[0095] The films may also be coated—preferably in an off-lineprocess—with metals, such as aluminum, or with ceramic materials, suchas SiO_(x) or Al_(x)O_(y). This in particular improves their gas-barrierproperties.

[0096] The polyester film of the invention preferably also comprises asecond outer layer C. The structure, thickness, and composition of thesecond outer layer may be selected irrespective of the other outer layerpresent, and the second outer layer may likewise comprise theabovementioned polymers, the UV stabilizer, the flame retardant, orpolymer mixtures for the base layer or the first outer layer of theinvention, but these do not have to be identical with those of the firstouter layer. The second outer layer may also comprise other commonlyused outer layer polymers, while these may also be provided with UVstabilizer and/or the flame retardant.

[0097] If desired, there may also be an intermediate layer between thebase layer and the outer layer(s). The intermediate layer may becomposed of the polymers described for the base layer. In oneparticularly preferred embodiment, it is composed of the polyester usedfor the base layer. It may also comprise the conventional additivesdescribed, and the flame retardant and/or the UV stabilizer. Thethickness of the intermediate layer is generally above 0.3 μm,preferably in the range from 0.5 to 15 μm, in particular from 1.0 to 10μm.

[0098] The thickness of the outer layer(s) is generally above 0.1 μm,preferably in the range from 0.2 to 5 μm, in particular from 0.2 to 4μm, and the thicknesses of the outer layers may be identical ordifferent.

[0099] The total thickness of the polyester film of the invention mayvary within wide limits and depends on the intended application. It ispreferably from 4 to 500 μm, in particular from 5 to 450 μm, withpreference from 6 to 300 μm, the base layer preferably making up fromabout 40 to 90% of the total thickness.

[0100] It is entirely surprising that the use of the abovementioned UVstabilizers in films led to the desired result. The skilled worker wouldprobably first have attempted to achieve UV resistance by using anantioxidant, but would have discovered that on weathering the filmrapidly yellows.

[0101] On using conventional UV stabilizers, the skilled worker wouldhave found that

[0102] the UV stabilizer has inadequate thermal stability and attemperatures of from 200 to 240° C. decomposes and evolves gases

[0103] large amounts of UV stabilizer would have had to have beenincorporated (from about 10 to 15% by weight) to absorb the UV light andprevent damage to the film.

[0104] At these high concentrations, the skilled worker would have foundthat the film becomes yellow just after it has been produced, withYellowness Index deviations (YI) around 25. The mechanical properties ofthe film would also have been found to be adversely affected.Orientation would have produced exceptional problems, such as

[0105] break-offs due to unsatisfactory strength, i.e. modulus ofelasticity too low;

[0106] die deposits, causing profile variations;

[0107] roller deposits from the UV stabilizer, causing immpairment ofoptical properties (poor haze, defective adhesion, non-uniform surface);

[0108] deposits in stretching frames or heat-setting frames, droppingonto the film.

[0109] It was therefore more than surprising that even lowconcentrations of the UV stabilizer of the invention achieve excellentUV protection. It was very surprising that, together with this excellentUV protection:

[0110] within the accuracy of measurement, the Yellowness Index of thefilm is unchanged from that of an unstabilized film;

[0111] there were no evolution of gases, no die deposits, and no framecondensation, and the film therefore has excellent optical propertiesand excellent profile and layflat;

[0112] the UV-resistant film has excellent stretchability, and cantherefore be produced in a reliable and stable manner on high-speed filmlines at speeds of up to 420 m/min.

[0113] It was also surprising that a flame-retardant film with therequired property profile can be produced cost-effectively and withoutcaking in the dryer by using masterbatch technology and suitablepredrying and/or precrystallization and, where appropriate, smallamounts of a hydrolysis stabilizer, and that the film does not embrittleby exposure to heat and does not break when folded.

[0114] It is moreover very surprising that it is also possible to reusethe recycled material (regrind) produced from the films withoutadversely affecting the Yellowness Index of the film.

[0115] The film of the invention can readily be recycled withoutpollution of the environment, and is therefore suitable for use asshort-lived advertising placards, in the construction of exhibitionstands, or for other short-lived promotional items, where fireprotection and UV absorption are desired.

[0116] Another advantage is that the production costs of the film of theinvention are only slightly higher than those for a film made fromstandard polyesters. The other properties of the film of the inventionrelevant to its processing and use are substantially unchanged or indeedhave been improved. In addition, it has been ensured that duringproduction of the film it is possible to reuse the regrind in aproportion of up to 50% by weight, preferably from 10 to 50% by weight,based in each case on the total weight of the film, without anysignificant resultant adverse effect on the physical properties of thefilm.

[0117] In summary, the film of the invention has flame retardancy to DIN4102 (construction materials classes B1 and B2), is impermeable to UVlight, is highly UV resistant, has low gloss, in particular low gloss onfilm surface A, and has comparatively low haze. It moreover has goodwinding and processing performance. It is also worthy of mention thatthe outer layer of the invention has good writability with respect toballpoint pen, felt-tip pen, or fountain pen.

[0118] The gloss of film surface A is lower than 70. In one preferredembodiment the gloss of this side is less than 60, and in oneparticularly preferred embodiment less than 50. This surface of the filmis therefore particularly effective for promotional purposes.

[0119] In addition, the film complies with construction materialsclasses B1 and B2 to DIN 4102 Part 1 and Part 2 and shows noembrittlement on exposure to heat. The Yellowness Index (YI) of the filmof the invention is not higher than that of a standard film. The filmbegins to transmit light or radiation at >360 nm, i.e. the film absorbsthe harmful UV radiation. A non-UV-resistant film transmits radiationfrom as low as 280 nm, i.e. the UV light in the wavelength region from280 to 360 nm is not absorbed but transmitted by the film.

[0120] The haze of the film of the invention is smaller than 40%. In onepreferred embodiment, the haze of the film is less than 35%, and in oneparticularly preferred embodiment less than 30%. The comparatively lowhaze of the film (compared with a matt monofilm, see comparativeexample) means that the 30 film can, for example, be reverse-printed, orviewing windows can be incorporated through which, for example, thecontents can be clearly discerned.

[0121] The combination of exceptional properties gives the film of theinvention excellent suitability for a wide variety of applications, forexample for interior decoration, for construction of exhibition standsor for exhibition requisites, as displays, for placards, for protectiveglazing of machinery or vehicles, in the lighting sector, in the fittingout of shops or of stores, as a promotional item, or laminating medium,for greenhouses, roofing systems, exterior cladding, protectivecoverings, applications in the construction sector, and illuminatedadvertising profiles, blinds, and electrical applications.

[0122] Other application sectors are its use for producing labels, as arelease film, or as a hot-stamping foil, or in-mold labeling.

[0123] The table below (Table 1) gives again the most important filmproperties of the invention. TABLE 1 inventive particularly rangepreferred preferred Unit Test method Gloss, side A <70 <60 <50 DIN 67530 (measurement angle 60) Haze <40 <35 <30 % ASTM D Coefficient offriction: DIN 53 375 Side A with respect to <0.6 <0.55 <0.50 itself SideB and, respectively, <0.5 <0.55 <0.55 C with respect to itself Averageroughness R_(a) 200-600 230-550 250-530 nm DIN 4768 (side A) with cutoffat 0.25 nm Yellowness Index (YI) <30 <20 <10 DIN 6167 High UV resistancePermeability to UV light >350 >360 >370 nm from wavelength Constructionmaterials complies class to DIN 4102 with B 2 Part 2 and Part 1 complieswith B 1

[0124] The methods used to characterize the polymers and the films wereas follows:

[0125] Test Methods

[0126] DIN=Deutsches Institut für Normung

[0127] ISO=International Organization for Standardization

[0128] ASTM=American Society for Testing and Materials

[0129] SV (DCA), IV (DVE)

[0130] Standard viscosity SV (DCA) is measured in dichloroacetic acid bya method 30 based on DIN 53726.

[0131] Intrinsic viscosity (IV) is calculated as follows from standardviscosity

IV(DCA)=6.67·10⁻⁴ SV(DCA)+0.118

[0132] Coefficient of Friction

[0133] Coefficient of friction is determined to DIN 53 375, 14 daysafter production.

[0134] Surface Tension

[0135] Surface tension was determined by what is known as the ink method(DIN 53 364).

[0136] Haze

[0137] Haze of the film was measured to ASTM D1003-52. The Hölz hazemeasurement was made by a method based on ASTM D1003-52, but in order toutilize the ideal measurement range was measured on four mutuallysuperimposed laps of film, and a 1° slit diaphragm was used instead of a4° pinhole.

[0138] Gloss

[0139] Gloss was determined to DIN 67 530. Reflectance was measured,this being an optical value characteristic of a film surface. Based onthe standard ASTM D523-78 and ISO 2813, the angle of incidence was setat 20 or 60. A beam of light hits the flat test surface at the set angleof incidence and is reflected and/or scattered by the surface. Aproportional electrical variable is displayed representing light rayshitting the photoelectric detector. The value measured is dimensionlessand must be stated together with the angle of incidence.

[0140] Roughness

[0141] The roughness R_(a) of the film was determined to DIN 4768 with acutoff of 0.25 mm.

[0142] Mechanical Properties

[0143] Modulus of elasticity and tensile strength at break, and tensilestrain at break, were measured longitudinally and transversely to ISO527-1-2.

[0144] Weathering (Bilateral), UV Resistance

[0145] UV resistance was tested as follows to the ISO 4892 testspecification: Test equipment Atlas Ci65 Weather-Ometer Test conditionsto ISO 4892, i.e. artificial weathering Irradiation time 1 000 hours(per side) Irradiation 0.5 W/m², 340 nm Temperature 63° C. RelativeHumidity 50% Xenon lamp internal and external filter made fromborosilicate 102 minutes of UV light, then 18 minutes of UV Irradiationcycles light with water spray on the specimens, then again 102 minutesof UV light, etc.

[0146] Numerical values of <0.3 can be disregarded and mean that nosignificant color change has occurred.

[0147] Yellowness Index

[0148] Yellowness Index (YI) is the deviation from colorlessness in the“yellow” direction and is measured to DIN 6167. Yellowness Indices(YIs)<5 are not visually detectable.

[0149] Each of the examples and comparative examples below concernstransparent films of varying thickness, produced on the extrusion linedescribed.

[0150] All of the films were weathered bilaterally, each for 1000 hoursper side, to the test specification ISO 4892 using the Atlas C165Weather-Ometer, and then tested for mechanical properties, YellownessIndex (YI), surface defects, light transmittance, and gloss.

[0151] The examples below provide illustration of the invention.

EXAMPLE 1

[0152] a) Preparation of Component II for the Outer Layer Mixture of theInvention

[0153] A copolyester having about 90 mol % of isophthalic acid and 10mol % of the sodium salt of 5-sulfoisophthalic acid as acid componentand 100 mol % of ethylene glycol as glycol component was prepared by thefollowing process:

[0154] A stainless steel reaction vessel of 2 I capacity, equipped withan anchor stirrer, a thermal element for measuring the temperature ofthe vessel contents, an 18 inch Claisen/Vigreux distillation column withcondenser and receiver, an inlet opening, and a heating jacket, waspreheated to 190° C. and flushed with nitrogen. 1065.6 g of dimethylisophthalate, 180.6 g of the sodium salt of dimethyl5-sulfoisophthalate, and 756.9 g of ethylene glycol were placed in thevessel. A buffer (Na₂CO₃ 10H₂O-0.439 g) and a transesterificationcatalyst (Mn(OAc)₂ 4H₂O-0.563 g) were also placed in a vessel. Themixture was heated with stirring, whereupon methanol distilled off.During the distillation the temperature in the vessel was graduallyincreased to 250° C. When the distillate weight corresponded to thetheoretical methanol yield, an ethylene glycol solution comprising 0.1889 of phosphorous acid was added. The distillation column was replaced bya curved vapor take-off with receiver. 20 g of pure ethylene carbonatewere added to the reaction mixture, whereupon vigorous evolution of gas(CO₂) began immediately. CO₂ evolution subsided after about 10 min. Areduced pressure of 240 mmHg was then applied, and the polycondensationcatalyst (0.563 g of Sb₂O₃ slurried in ethylene glycol) was added. Thereaction mixture was stirred for 10 min while the reduced pressure of240 mmHg was maintained, and then the pressure was further reduced tofrom 240 to 20 mmHg in steps of 10 mmHg/min. As soon as the pressure inthe system had been reduced to 20 mmHg, the temperature in the vesselwas raised from 250 to 290° C. at a rate of 2 C/min. When thetemperature in the vessel had reached 290° C. the stirrer speed wasthrottled back and the pressure was reduced to not more than 0.1 mmHg.At this juncture a read-out was obtained from the stirrer motor using anammeter. The viscosity of the polymer was controlled by allowing thepolycondensation to proceed in accordance with set values for the changein the ampere value from the stirrer motor of (in each case) 2.3 A. Whenthe desired molecular weight had been achieved, nitrogen pressure wasapplied to the vessel to expel the liquid polymer from the outlet in thebase of the vessel into an ice-water quenching bath.

[0155] B) Preparation of the Mixture for Outer Layer A of the Invention

[0156] 75% by weight of component I (polyethylene terephthalate with SVof 680) were fed to the inlet hopper of a twin-screw extruder with 15%by weight of component II and 10% by weight of a masterbatch whichcomprises the UV stabilizer, and the two components were extrudedtogether at about 300° C. and fed to the outer layer channel A of acoextrusion die.

[0157] The masterbatch is composed of 5% by weight of2-(4,6-diphenyl-1,3,5-triazin-2-yl)-5-hexyloxyphenol (®TINUVIN 1577) asUV stabilizer and 95% by weight of polyester.

[0158] Base Layer B:

[0159] The predried flame retardant is metered in the form of amasterbatch into the base layer.

[0160] The flame retardant masterbatch is composed of 20% by weight offlame retardant and 80% by weight of polyester.

[0161] The flame retardant is the organophosphorus compound dimethylmethylphosphonate ®Amgard P1045 from the company Albright & Wilson,which is soluble in the polyester.

[0162] The composition of the base layer is as follows: 75% by weight ofpolyethylene terephthalate (RT 49 from Hoechst AG) with SV of 800 and 5% by weight of masterbatch made from 99% by weight of polyethyleneterephthalate and 1.0% by weight of silica particles (® Sylobloc 44 Hfrom the company Grace) with average particle size of 4.5 μm 20% byweight of the flame retardant masterbatch.

[0163] The components of the base layer are charged at room temperaturefrom separate feed vessels into a vacuum dryer which prior to thejuncture of charging until the end of the residence time traverses atemperature profile of from 25 to 130° C. The raw material mixture isstirred at 61 rpm during the residence time of 4 hours.

[0164] The precrystallized or predried raw material mixture ispost-dried in the downstream hopper, likewise in vacuo, at 140° C. for 4hours, and fed to the extruder for the base layer.

[0165] Outer Layers A and C:

[0166] Chips made from polyethylene terephthalate and from a filler werelikewise fed to the extruder for the outer layer C. A transparentthree-layer film with ABC structure and total thickness 12 μm was thenproduced by coextrusion followed by stepwise longitudinal and transverseorientation. The thickness of each of the outer layers was 1.5 μm. Outerlayer A: 75% by weight of component I 15% by weight of component II, and10% by weight of UV masterbatch (5% by weight of ® TINUVIN 1577, 95% byweight of polyester) Outer layer C 80% by weight of polyethyleneterephthalate (RT 49 from Hoechst AG) with SV of 800 and 10% by weightof masterbatch made from 99% by weight of polyethylene terephthalate and1.0% by weight of silica particles (® Sylobloc 44 H from the companyGrace) with an average particle size of 4.5 μm, and 10% by weight of UVmasterbatch (5% by weight of ® TINUVIN 1577, 95% by weight of polyester)

[0167] The individual steps of the process were: LongitudinalTemperature: 85-135° C. stretching Longitudinal stretching ratio: 4.0:1Transverse Temperature: 85-135° C. stretching Transverse stretchingratio: 4.0:1 Setting Temperature:   230° C.

EXAMPLE 2

[0168] In a manner similar to that of Example 1, a three-layer film witha total thickness of 12 μm was produced by coextrusion. Only thecomposition of outer layer A was changed:

[0169] Outer Layer A:

[0170] 70% by weight of component I

[0171] 20% by weight of component 11, and

[0172] 10% by weight of UV masterbatch.

EXAMPLE 3

[0173] A coextruded film using the mixing specification of Example 1, inwhich the composition of outer layer A was as follows:

[0174] 65% by weight of component I

[0175] 25% by weight of component II, and 10% by weight of UVmasterbatch.

EXAMPLE 4

[0176] A coextruded film using the mixing specification of Example 1, inwhich the composition of outer layer A was as follows:

[0177] 55% by weight of component I

[0178] 35% by weight of component II, and

[0179] 10% by weight of UV masterbatch.

COMPARATIVE EXAMPLE

[0180] A monofilm was produced and had the composition of outer layer Afrom Example 3. The film surfaces had the required mattness, but thefilm did not meet the set requirements because it had excessive haze. Itwas also very difficult to produce the film by a process which wasreliable and therefore cost-effective.

[0181] The film is moreover not UV-resistant and transmits the harmfulUV light. After 1000 hours of weathering the film exhibits cracks andembrittlement phenomena, and also visible yellowing. The film is notcompliant with construction material classes B1 and B2. TABLE 2 GlossCompliant with (60° Permeability construction Film Outer layermeasurement to Ex. material classes thickness thickness structure angle)radiation No. to DIN 4102 (μm) A/C(μm) structure Side A Side C Haze (nm)1 B1 and B2 12 1.5/1.5 ABC 65 175 25 >360 2 B1 and B2 12 1.5/1.5 ABC 55175 26 >360 3 B1 and B2 12 1.5/1.5 ABC 45 175 28 >360 4 B1 and B2 121.5/1.5 ABC 35 175 30 >360 CE 12 A 35 160 70 >280

[0182] After 1000 hours of weathering using the Atlas CI65Weather-Ometer the films of Examples 1-4 do not show any kind ofembrittlement or cracking, and their Yellowness Indices are <10.

1. A coextruded, biaxially oriented polyester film composed of a baselayer and of at least one outer layer, where the film comprises, asflame retardant, at least one organic phosphorus compound soluble inthermoplastics, and further comprises at least one UV stabilizer andwherein the film has a matt outer layer which comprises a mixture or ablend or a mixture and a blend made from two components I and II, wherecomponent I is essentially a polyethylene terephthalate homopolymer orpolyethylene terephthalate copolymer or a mixture made from polyethyleneterephthalate homopolymer or from polyethylene terephthalate copolymers,and component II is a polymer which is a condensation product of thefollowing monomers or of their derivatives capable of forming polymersor of the following monomers and of their derivatives capable of formingpolymers: A) from about 65 to about 95 mol % of isophthalic acid, B)from 0 to about 30 mol % of at least one aliphatic dicarboxylic acidwith the formula HOOC(CH₂)_(n)COOH where n is from 1 to 11; C) fromabout 5 to about 15 mol % of at least one sulfomonomer containing analkali metal sulfonate group on the aromatic moiety of an aromaticdicarboxylic acid; D) a copolymerizable aliphatic or cycloaliphaticglycol having from 2 to 11 carbon atoms, in the stoichiometric amountnecessary to form about 100 mol % of condensate; where each of thepercentages given is based on the total amount of the monomers formingcomponent II.
 2. The film as claimed in claim 1, wherein the ratio ofcomponents I and II is in the range from II:I=about 10:about 90 toI:II=about 95:about
 5. 3. The film as claimed in claim 1, wherein the UVstabilizer is selected from the group consisting of2-hydroxybenzotriazoles, triazines and mixtures of these.
 4. The film asclaimed in claim 1, wherein the concentration of the flame retardant isfrom about 0.5 to about 30.0% by weight, based on the weight of thecrystallizable thermoplastic.
 5. The film as claimed in claim 4, whereinthe concentration of the flame retardant is from about 1.0 to about20.0% by weight, based on the weight of the crystallizablethermoplastic.
 6. The film as claimed in claim 1, wherein the flameretardant comprises organophosphorus compounds.
 7. The film as claimedin claim 6, wherein the flame retardant comprises carboxyphosphinicacids, or anhydrides of these.
 8. The film as claimed in claim 1,wherein additionally a hydrolysis stabilizer is present in the form of aphenolic stabilizer or one or more of alkali metal stearate, alkalineearth metal stearate, alkali metal carbonate and alkaline earth metalcarbonate in amounts of from about 0.01 to about 1.0% by weight.
 9. Thefilm as claimed in claim 8, wherein the hydrolysis stabilizer is aphenolic stabilizer in amounts of from about 0.05 to about 0.6% byweight.
 10. The film as claimed in claim 9, wherein, the amount is fromabout 0.15 to about 0.3% by weight, and the hydrolysis stabilizer has amolar mass above about 500 g/mol.
 11. The film as claimed in claim 8,wherein the hydrolysis stabilizer is pentaerythrityltetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate or 1,3,5-trimethyl-2,4,6,-tris(3,5-di-tert-butyl-4-hydroxybenzyl )-benzene orpentaerythrityl tetrakis-3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionateand1,3,5-trimethyl-2,4,6,-tris(3,5-di-tert-butyl-4-hydroxybenzyl)-benzene.12. The film as claimed in claim 1, wherein the outer layer has athickness of from about 0.2 to about 6 μm.
 13. The film as claimed inclaim 1, wherein the film has two layers and is composed of the baselayer and of the outer layer.
 14. The film as claimed in claim 1,wherein the film has three layers and is composed of the base layer andof an outer layer on each side of the base layer.
 15. The film asclaimed in claim 13 or 14, wherein an outer layer comprises an inorganicfiller.
 16. The film as claimed in claim 1, wherein at least one surfaceof the film is metallized or is coated with SiO_(x), Al_(x)O_(y),ethylvinyl alcohol, PVDC, waterglass, hydrophilic polyester, vinylacetate, polyvinyl acetate, poly-urethane, fatty acid salts of alkalimetals or of alkaline earth metals, butadiene copolymer, (meth)acrylicacid or esters thereof, or silicone.
 17. A process for producing a filmas claimed in claim 1, in which polyester melts corresponding to thecompositions of the outer and base layers are fed to a coextrusion die,and extruded from the die onto a chill roll, and the resultant prefilmis then biaxially oriented and heat-set, where the polyester melts forone or more of the base layer and the outer layer comprise at least oneor more of UV stabilizer and flame retardant, and the polyester melt forthe outer layer comprises a mixture or a blend or a mixture and a blendmade from two components I and II, where component I is a polyethyleneterephthalate homopolymer or polyethylene terephthalate copolymer or amixture made from polyethylene terephthalate homo- or copolymers andcomponent II is a polymer which contains at least one sulfonate group.18. A method of making an interior decoration, a display, a placards, aprotective glazing, a shop outfit, a promotional requisite, a laminatingmedium, an exterior cladding, a protective covering, an illuminatedadvertising profile, or a blind, which comprises converting a film asclaimed in claim 1 into an interior decoration, a display, a placards, aprotective glazing, a shop outfit, a promotional requisite, a laminatingmedium, an exterior cladding, a protective covering, an illuminatedadvertising profile, or a blind.
 19. A method of making a label whichcomprises converting a film as claimed in claim 1 into a label.
 20. Amethod of making a release film for producing glass-fiber-reinforcedsemifinished products which comprises converting a film as claimed inclaim 1 into a release film.
 21. A method of making a hot-stamping foilwhich comprises converting a film as claimed in claim 1 into ahot-stamping foil.
 22. A method of making an in-mold label whichcomprises converting a film as claimed in claim 1 into an in-mold label.